During the useful life of a gas turbine, maintenance operations are necessary for guaranteeing the correct functioning of the turbine itself. During these periodical operations, controls and inspections are done and damaged or worn parts or components are substituted.
The parts of a turbine which are most subject to wear are the turbine blades as they undergo mechanical stress at a high temperature and are also subject to hot corrosion due to the hot gases with which the turbine operates. Therefore, there exists the necessity of periodical inspections of the turbine blades to control their integrity and functionality. During programmed maintenance operations, in order to be able to inspect the blades of the turbine, it is usually necessary to rotate the blades of the turbine, which is done by rotating the whole turbine rotor. This is applied especially in the case of a boroscopic inspection, where the turbine is opened, decoupled from the compressor, so that the blades can then be inspected by means of a boroscope.
Large turbomachinery rotors, particularly of large gas turbines, need to be rotated at a very low rotational speed and to an exact positioning during boroscopic inspection in order to precisely carry out operations on the rotor, such as mechanical rotor maintenance, rotor balancing or rotor alignment. Typically, boroscopes are used for this kind of inspection work, where the area to be inspected is inaccessible by other means: boroscopes are optical devices comprising illuminating means for the illumination of the remote object to be inspected, such that an internal image of the illuminated object is obtained and is further magnified to be presented to the viewer's eyes.
Boroscopes are commonly used in the visual inspection of industrial gas turbines, as gas turbines require particular attention because of safety and maintenance requirements. Boroscope inspection can be used to prevent unnecessary maintenance, which can become extremely costly for large gas turbines.
Typically, at present, the required rotation of the rotor of a gas turbine for boroscopic inspection is carried out manually, such that a person manually rotates the rotor; however, this task is not accurate when performed.
One disadvantage of this method is that it takes longer for inspecting the blades, representing a considerable cost as it reduces the productivity of the turbine itself. In addition to this cost, there is the cost of labour.
Different boroscope devices used for the inspection of turbomachines are is known in the state of the art. For example, document EP 2495553 A2 discloses a portable boroscope assembly used for the inspection of turbomachine blades. Also known in the art is document US 2012/0204395 A1 (issued as U.S. Pat. No. 8,910,359), disclosing a method for inspecting and/or repairing a component in a gas turbine engine, by using a boroscope. Also, document US 2012/0285226 A1 (issued as U.S. Pat. No. 8,695,445) discloses a system having a wear-indicating mark applied to a portion of surface of an internal component in a turbine, this mark being visually discernible through boroscopic inspection. Also known in the art, as per document EP 1749979 A2, is a movement system comprising a crank rotation mechanism having a reducer group for rotating, in particular manually, the shaft of the turbine to allow the inspection of blades by means of a boroscope, avoiding at the same time the necessity of decoupling said turbine from the compressor. However, all these documents of the prior art that have been cited move the rotor (shaft) of the turbine manually, therefore being not accurate and being costly and time consuming.
Another system for rotating a shaft of a turbine, known in the art, is for example the one shown in document U.S. Pat. No. 4,193,739, where a device for turning a rotor of a gas turbine engine is disclosed for inspection purposes, comprising a nozzle that directs a jet of air onto the blades to turn the rotor. Also, the device comprises a rod that can move axially and that can stop the rotor. However, this system is not accurate and also requires human exertion, which makes it costly and time consuming. Also, this system is not able to provide a variable speed control on the rotor speed, in order to accurately effect boroscopic inspections in the gas turbine.
The present invention is directed towards providing the above-mentioned needs.